At four o'clock on the morning of 7 December 1941, two U. S. Army signalmen switched on the radar at their station near the northernmost point of Oahu. They would be on duty until seven, when a truck would call to take them back to the post for breakfast. The rest of the day would be theirs, for it was Sunday, and the big SCR-270 radar would be closed down until the next early morning shift. Along with five other mobile stations spotted around the perimeter of the island until the permanent sites could be made ready, the Opana radar was intended to operate for two hours before dawn and one afterward, according to the latest operating schedule agreed upon under the past week's alert.